Splitting Of States Research Articles

Heat capacities and thermodynamic functions of neodymia and samaria doped ceria

Doped ceria materials are ionic conductors currently under investigation for use in solid oxide fuel cells, catalysts, and other applications. We measured the heat capacity of several doped ceria samples from 1.8 K to 300 K to better understand their physical properties. The samples used in this study were either singly doped with Nd or Sm, or co-doped with both Nd and Sm. This work complements an earlier detailed study of their heats of formation and ionic conductivity. Here we provide the thermodynamic functions based on theoretical fits of our heat capacity measurements including Cp,m°, Δ0TSm°, Δ0THm°, and Φm°. We also detected splitting of nuclear magnetic states, which appeared as an upturn in the heat capacity below 10 K. We observed this phenomenon in all samples and provide calculations of the local magnetic field causing the splitting.

Markov invariant dynamics

We consider, M(I), a certain class of Markov interval maps with domain contained in the interval I, whose associated transition matrix Af, necessarily primitive, plays a crucial role in the study of the underlying dynamics.We study the problem of deciding when a restriction g:=f|J of a map f∈M(I) to a subset J⊂I is in the class M([J]), where [J] is the minimal closed interval containing J. We establish natural conditions on J⊂I so that g=f|J is a Markov map. Then we tackle the central problem of deciding when the matrix Ag is primitive in this framework. We are able to enumerate the sets J, satisfying the referred conditions, through a systematic process of elimination of the rows/columns of the state splitting of Af associated to the so called removable states, which ensures the primitivity of the matrices Ag.

Growth and Characterization of TiO2 Thin Films by PLD Technique

In this work, the structural, optical and electronic properties of TiO2 thin films grown on glass substrate by Pulse Laser Deposition (PLD) technique are presented. The stoichiometry and the oxidation degree of films were analyzed by considering the Ti 2p and O 1s core energy levels with high resolution X-Ray Photoelectron spectroscopy (XPS). The structural characteristics of the thin films have been investigated by X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) technique. The optical absorption region of growth TiO2 films were analyzed by Photoluminescence spectroscopy (PL) technique. Spin-orbit coupling splitting of Ti 2p states was measured as 5.7 eV. The characterizations promote the existence of the metal and oxygen vacancies at the surface of film. These point defects enhance the hysteretic transport properties of the TiO2 metal oxide.

Decomposing Magnetic Dark-Field Contrast in Spin Analyzed Talbot-Lau Interferometry: A Stern-Gerlach Experiment without Spatial Beam Splitting.

We have recently shown how a polarized beam in Talbot-Lau interferometric imaging can be used to analyze strong magnetic fields through the spin dependent differential phase effect at field gradients. While in that case an adiabatic spin coupling with the sample field is required, here we investigate a nonadiabatic coupling causing a spatial splitting of the neutron spin states with respect to the external magnetic field. This subsequently leads to no phase contrast signal but a loss of interferometer visibility referred to as dark-field contrast. We demonstrate how the implementation of spin analysis to the Talbot-Lau interferometer setup enables one to recover the differential phase induced to a single spin state. Thus, we show that the dark-field contrast is a measure of the quantum mechanical spin split analogous to the Stern-Gerlach experiment without, however, spatial beam separation. In addition, the spin analyzed dark-field contrast imaging introduced here bears the potential to probe polarization dependent small-angle scattering and thus magnetic microstructures.

Verifiable Structure of Technological Processes in Dynamic 3D Models of Railway Stations

The article is devoted to the study of technological processes at railway stations reproduced in a threedimensional model from the standpoint of assessing reliability of the development of those processes. The identifiable simulated and virtual processes are matched against specific comparative positions. The benchmark is a fixed set of technological series of operations for processing wagon flows of all categories at a particular railway station.To provide adequacy of model reconstruction to the prototype, the emerging waiting time and downtime of rolling stock are considered, which are introduced into the model as special split states of main spatial locations of rolling stock. The concept of «paraphysical structures» is introduced into the developed model of the station, which comprises any conditions impossible according to physical canons and irrational according to technological requirements regarding the objects of track development and rolling stock. The logic of program control over similar states of modelled structures is based on the analysis of the allowed positions of station objects when performing reference technological operations. Slowdown in station operations can be a forerunner to waiting or downtime.An important methodological basis for the technique for developing a dynamic model of a station includes formation of a system of internal program analysis of the current situation, recognition of the moment of occurrence of a paraphysical situation and its anticipation by transforming it into normally developing standard situation. The adapting module of the information prototyping environment should be an intelligent agent with developed ability of generating exceptional situations based on comparative tests conducted by it, of developing an appropriate knowledge base and of using it in the process of further operations without any external users’ participation.The objective of the study, described in the article, is associated with dev elopment of general requirements for a dynamic model of a railway station, functioning adequately to a real technical system due to assessment of reliability of reproduced station technological processes.

Sn-V centers in diamond activated by ultra high pressure and high temperature treatment

We investigate the activation of Sn-V centers in diamond through ions implantation and the subsequent high pressure and high temperature (HPHT) treatment at 15 GPa and 2300 °C. Sn ions is implanted at fluences greater than 2 × 1014 cm−2 by varying the acceleration voltage up to 180 kV, which results in a Sn distribution with a uniform concentration of 1 × 1020 cm−3 down to a depth of 50 nm from the surface. The subsequent HPHT treatment recovers the transparent appearance and preserves the introduced Sn ions. The sample shows emission peaks composed of four levels that originate from the Sn-V centers. The two distinct emission peaks from the lower excited states to the split ground states are stable up to 77 K. At 10 K, these peaks are clearly observable at excitation powers spanning two orders of magnitude, which suggests the preferential carrier capture at these centers.

Oxygen-redox reactions in LiCoO2 cathode without O–O bonding during charge-discharge

Summary Oxygen activity in highly delithiated LiCoO2 is critical to fully utilizing the energy density of this high-tap-density cathode but still lacks a clear understanding. In this work, we combined the results of several experimental techniques, especially resonant inelastic X-ray scattering (RIXS) and neutron pair distribution function (NPDF) analysis, together with theoretical calculations to study this topic. Our results conclude that oxygen redox takes place globally in the lattice, rather than forming localized dimerization as previously thought. RIXS results directly reveal the reversible oxygen redox, and NPDF results show that the O–O pair distance is considerably shortened in the highly delithiated LiCoO2. Theoretical calculations indicate that no O–O bonding is formed in LiCoO2, in sharp contrast to the lithium-rich system in which O–O bonding does form. These results provide the rationale for achieving a reversible deep delithiation and high energy density for LiCoO2-based electrodes.

Multichannel Topological Transport in an Acoustic Valley Hall Insulator

Valley interface states, resulting in acoustic valley Hall topological insulators, have recently become a hot topic in the study of acoustic systems. On the basis of structural diversity and potential applications, we construct a two-dimensional triangular-lattice phononic crystal with ${C}_{3v}$-symmetric scatterers, and obtain two distinct valley Hall phases with nonvanishing valley Chern indices by rotating the scatterers. We numerically calculate the dispersion relations of these valley Hall phases including two kinds of interfaces, and find that valley interface states exist at not only the zigzag interface but also the armchair interface. We demonstrate the acoustic splitting and merging of valley interface states in the cross-waveguides, and numerically achieve the xor and or logic functions. We also design three complicated waveguides by assembling phononic crystals with distinct valley Hall phases. By experimental measurements in these waveguides, we successfully implement one-, two-, and three-channel topological transport. This research possibly provides a design route exploiting valley interface states to fabricate multichannel acoustic communication devices.

Oxygen vacancy induced site-selective Mott transition in LaNiO3

While defects such as oxygen vacancies in correlated materials can modify their electronic properties dramatically, understanding the microscopic origin of electronic correlations in materials with defects has been elusive. Lanthanum nickelate with oxygen vacancies, LaNiO$_{3-x}$, exhibits the metal-to-insulator transition as the oxygen vacancy level $x$ increases from the stoichiometric LaNiO$_3$. In particular, LaNiO$_{2.5}$ exhibits a paramagnetic insulating phase, also stabilizing an antiferromagnetic state below $T_N\simeq152$K. Here, we study the electronic structure and energetics of LaNiO$_{3-x}$ using first-principles. We find that LaNiO$_{2.5}$ stabilizes a vacancy-ordered structure with an insulating ground state and the nature of the insulating phase is a "site-selective" paramagnetic Mott state as obtained using density functional theory plus dynamical mean field theory (DFT+DMFT). The Ni octahedron site develops a Mott insulating state with strong correlations as the Ni $e_g$ orbital is half-filled while the Ni square-planar site with apical oxygen vacancies becomes a band insulator. Our oxygen vacancy results can not be explained by the pure change of the Ni oxidation state alone within the rigid band shift approximation. Our DFT+DMFT density of states explains that the peak splitting of unoccupied states in LaNiO$_{3-x}$ measured by the experimental X-ray absorption spectra originates from two nonequivalent Ni ions in the vacancy-ordered structure.

A classification of pure states on quantum spin chains satisfying the split property with on-site finite group symmetries

We consider a set S P G ( A ) SPG(\mathcal {A}) of pure split states on a quantum spin chain A \mathcal {A} which are invariant under the on-site action τ \tau of a finite group G G . For each element ω \omega in S P G ( A ) SPG(\mathcal {A}) we can associate a second cohomology class c ω , R c_{\omega ,R} of G G . We consider a classification of S P G ( A ) SPG(\mathcal {A}) whose criterion is given as follows: ω 0 \omega _{0} and ω 1 \omega _{1} in S P G ( A ) SPG(\mathcal {A}) are equivalent if there are automorphisms Ξ R \Xi _{R} , Ξ L \Xi _L on A R \mathcal {A}_{R} , A L \mathcal {A}_{L} (right and left half infinite chains) preserving the symmetry τ \tau , such that ω 1 \omega _{1} and ω 0 ∘ ( Ξ L ⊗ Ξ R ) \omega _{0}\circ \left ( \Xi _{L}\otimes \Xi _{R}\right ) are quasi-equivalent. It means that we can move ω 0 \omega _{0} close to ω 1 \omega _{1} without changing the entanglement nor breaking the symmetry. We show that the second cohomology class c ω , R c_{\omega ,R} is the complete invariant of this classification.

Flat bands in twisted bilayers of polar two-dimensional semiconductors

We investigate the Bloch flat bands in twisted bilayers from nonpolar to polar two-dimensional semiconductors using first-principles calculations and density functional based tight-binding simulations. First, to delineate the underlying mechanism of the formation of the flat bands, we rely on a tight-binding model of modified graphene where a bias between the A-B sublattice of the hexagonal lattice is introduced. By analyzing the evolution of the valence and conduction band edges of the bilayer of the modified graphene with different stacking patterns, a mechanism attributed to the splitting of the defect-like band edge states induced by different stacking patterns is revealed. The magic angle mechanism is no longer needed. Next, guided by the revealed mechanism, we predict the formation of flat bands in twisted bilayers of a series of two-dimensional systems from nonpolar to polar semiconductors. Our finding has important implications for exploring the flat band physics in low dimensions.

Classical and cubic Rashba effect in the presence of in-plane 4f magnetism at the iridium silicide surface of the antiferromagnet GdIr2Si2

We present a combined experimental and theoretical study of the two-dimensional electron states at the iridium-silicide surface of the antiferromagnet ${\mathrm{GdIr}}_{2}{\mathrm{Si}}_{2}$ above and below the N\'eel temperature. Using angle-resolved photoemission spectroscopy (ARPES) we find a significant spin-orbit splitting of the surface states in the paramagnetic phase. By means of ab initio density-functional-theory (DFT) calculations we establish that the surface electron states that reside in the projected band gap around the $\overline{\mathrm{M}}$ point exhibit very different spin structures which are governed by the conventional and the cubic Rashba effect. The latter is reflected in a triple spin winding, i.e., the surface electron spin reveals three complete rotations upon moving once around the constant energy contours. Below the N\'eel temperature, our ARPES measurements show an intricate photoemission intensity picture characteristic of a complex magnetic domain structure. The orientation of the domains, however, can be clarified from a comparative analysis of the ARPES data and their DFT modeling. To characterize a single magnetic domain picture, we resort to the calculations and scrutinize the interplay of the Rashba spin-orbit coupling field with the in-plane exchange field, provided by the ferromagnetically ordered $4f$ moments of the near-surface Gd layer.

Magnetic response and electronic states of well defined Graphene/Fe/Ir(111) heterostructure

We investigate a well defined heterostructure constituted by magnetic Fe layers sandwiched between graphene (Gr) and Ir(111). The challenging task to avoid Fe-C solubility and Fe-Ir intermixing has been achieved with atomic controlled Fe intercalation at moderate temperature below 500 K. Upon intercalation of a single ordered Fe layer in registry with the Ir substrate, an intermixing of the Gr bands and Fe $d$ states breaks the symmetry of the Dirac cone, with a downshift in energy of the apex by about 3 eV, and well-localized Fe intermixed states induced in the energy region just below the Fermi level. First principles electronic structure calculations show a large spin splitting of the Fe states, resulting in a majority spin channel almost fully occupied and strongly hybridized with Gr $\ensuremath{\pi}$ states. X-ray magnetic circular dichroism on the Gr/Fe/Ir heterostructure reveals an ordered spin configuration with a ferromagnetic response of Fe layer(s), with enhanced spin and orbital configurations with respect to the bcc-Fe bulk values. The magnetization switches from a perpendicular easy magnetization axis when the Fe single layer is lattice matched with the Ir(111) surface to a parallel one when the Fe thin film is almost commensurate with graphene.

Functional THz emitters based on Pancharatnam-Berry phase nonlinear metasurfaces

Recent advances in the science and technology of THz waves show promise for a wide variety of important applications in material inspection, imaging, and biomedical science amongst others. However, this promise is impeded by the lack of sufficiently functional THz emitters. Here, we introduce broadband THz emitters based on Pancharatnam-Berry phase nonlinear metasurfaces, which exhibit unique optical functionalities. Using these new emitters, we experimentally demonstrate tunable linear polarization of broadband single cycle THz pulses, the splitting of spin states and THz frequencies in the spatial domain, and the generation of few-cycle pulses with temporal polarization dispersion. Finally, we apply the ability of spin control of THz waves to demonstrate circular dichroism spectroscopy of amino acids. Altogether, we achieve nanoscale and all-optical control over the phase and polarization states of the emitted THz waves.

Prediction of structural, electronic and magnetic properties of full Heusler alloys Ir2YSi (Y = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) via first-principles calculation

First principles electronic structural calculation of full Heusler alloys Ir2YSi (Y= Sc to Ni) in the L21 (Cu2MnAl) and Xa (Hg2CuTi) structures have been studied using full-potential linearized augmented plane wave method (FP-LAPW) based on density functional theory (DFT). From the total energy calculations, it has been observed that all these alloys are stable in L21 structure than Xa structure and also it is found that the alloys Ir2YSi (Y =V to Co) are ferromagnetically stable whereas the Ir2YSi (Y = Sc, Ti, and Ni) alloys are non-magnetic in their stable L21 structure. Spin polarized band structure calculations reveal that in Ir2YSi (Y= V to Co) alloys there is spin splitting of energy states around the Fermi level (EF) indicating ferromagnetism and moreover in Ir2YSi (Y = V, Cr, and Mn) alloys majority electrons have metallic behavior while minority electrons have semiconducting nature exhibiting half metallic ferromagnetic (HMF) nature. HMF property in Ir2YSi (Y = V, Cr, and Mn) alloys have been further confirmed from the integer total magnetic moment value of 3.0 µB, 4.0 µB and 5.0 µB per formula unit respectively. Spin polarization mainly arises from the interaction between 3d electrons of V/Cr/Mn atom and 5d electrons of Ir atom. This strong d-d hybridization between the transition atoms like Ir and V/Cr/Mn composing Heusler alloys is essential for the formation of gap at the EF between the valence and conduction bands. Our results show that Ir2YSi (Y= V, Cr, and Mn) will be suitable for ferromagnetic and spintronics applications.

High-temperature and high-pressure Raman spectra of Fo89Fa11 and Fo58Fa42 olivines: Iron effect on thermodynamic properties

AbstractThe intrinsic anharmonicity plays an important role in the thermodynamic properties of minerals at the high-temperature conditions of the mantle. To investigate the effect of iron on the thermodynamic properties of olivine, the most abundant mineral in the upper mantle, we collected in situ high-temperature and high-pressure Raman spectra of natural Fo89Fa11 and synthetic Fo58Fa42 samples. Fo58Fa42 dissociates to enstatite + quartz + Fe2O3(+Fe) at 893 K. All the Raman-active modes systematically shift to lower frequencies at elevated temperatures, whereas to higher frequencies with increasing pressure. The Ag mode at ~960 cm–1 is more sensitive to the variations of temperature and pressure than other internal modes. The crystal-field splitting of the vibrational energy states becomes slightly weakened at high temperatures but strengthened at elevated pressures. We calculated the isobaric (γiP) and isothermal (γiT) mode Grüneisen parameters for these olivine samples. The intrinsic anharmonic parameters (ai) are negative for both the lattice and internal vibrations, and our calculations indicate that the intrinsic anharmonicity makes positive contributions to the thermodynamic properties of olivine at high temperatures, such as the internal energy (U), heat capacities (CV and CP), and entropy (S). Iron incorporation further increases the magnitudes of these anharmonic contributions. In addition, the Fe effect on the intrinsic anharmonicity may also apply to other thermodynamic properties in olivine, such as equations of state and equilibrium isotopic fractionations, which are important in constraining physical and chemical properties of the upper mantle.

Спектр высокого разрешения полос ν-=SUB=-2-=/SUB=-+ν-=SUB=-4-=/SUB=- (F-=SUB=-1-=/SUB=-,F-=SUB=-2-=/SUB=-) и 2ν-=SUB=-4-=/SUB=- (F-=SUB=-2-=/SUB=-) дейтерированного силана -=SUP=-28-=/SUP=-SiD-=SUB=-4-=/SUB=-

A study of the fine rotational structure of the silane molecule absorption spectrum was carried out for the first time. The high-resolution spectrum of 28SiD4 was recorded in the 1260-1480 cm-1 spectral range the vibrational ν2+ν4 (F1,F2) and 2ν4 (F2) bands were theoretically analyzed. Rotational, centrifugal distortion, tetrahedral splitting and resonance interaction parameters of the upper vibrational states were obtained from the weighted least square fit method. The set parameters obtained reproduces the initial vibrational-rotational structure of the ν2 + ν4 (F1, F2) and 2ν4 (F2) bands with an accuracy of drms = 3.9 · 10-4 cm-1.

Dark initial state radiation and the kinetic mixing portal

Data from Planck measurements of the cosmic microwave background (CMB) place important constraints on models with light dark matter (DM) and light mediators especially when both lie in the mass range below ∼ 1 GeV. In models involving kinetic mixing where the dark photon acts as the mediator, these constraints are easily satisfied and the appropriate DM relic density achievable if the DM is, e.g., a complex scalar, where p-wave annihilation occurs, or is the lighter component of a split pseudo-Dirac state where co-annihilation dominates. In both of these cases, although higher order in the dark gauge coupling, gD, the corresponding annihilation processes including dark photon initial state radiation (ISR) will be dominantly s-wave with essentially temperature independent cross sections. The rates for these dark ISR associated processes, though not yielding cross sections large enough to contribute to the relic density, can still run into possible conflicts with the bounds arising from the CMB. In this paper we perform a preliminary study of the present and potential future constraints that the CMB imposes on the parameter spaces for both of these scenarios due to the existence of this dark ISR. Further analyses of the effects of dark ISR in DM annihilation is clearly warranted.

Observations of Ultrafast Superfluorescent Beatings in a Cesium Atomic Vapor Excited by Femtosecond Laser Pulses

Picosecond and femtosecond superfluorescent beatings are observed from a dense atomic vapor. Cesium atoms are excited by femtosecond laser pulses via two-photon processes into their coherent superpositions of the ground 6S and excited 8S states. The yoked superfluorescent blue light at lower transitions of 6S - 7P is recorded and studied. Delayed buildup time of this blue light is measured as a function of the input laser beam power using a high-resolution 2 ps streak camera. At low power and density, a beating with a period of 100 picoseconds representing the ground state splitting is observed. The autocorrelation measurements of the generated blue light exhibit a beating with a quasi-period of 230 fs corresponding to the splitting of the 7P level. Understanding and, eventually, controlling the intriguing nature of superfluorescent beatings may permit a rapid quantum operation free from the rather slow spontaneous emission processes from atoms and molecules.

On the Reciprocal Mechanism of English as a Lingua Franca Participating in the Re-Generation of Sinitic Culture

The spread of English from a foreign language (EFL) to a lingua franca (ELF), underpinned by American culture, Anglophone culture, Western culture and the orientation of cultural universalism within the sphere of China and the Sinitic world, has been producing three linguistic-cultural circles: the outer is ELF and the culture; the superficial is the official Mandarin Chinese as a lingua franca (CLF) that represents the mainstream/dominant culture and political unification; and the inner, the vernacular/indigenous dialects/languages (VDL) that stand for sub/co-cultures and multi-culturalism. The movements, including clash and co-existence, of the three circles have generated two dynamic mechanisms within the re-generative paradigm of Sinitic cultural ecology: one is the assimilative mechanism and the other is the rejective mechanism. The two mechanisms, in turn, have operated among the three circles. The three circles and two mechanisms are functioning and re-shaping the on-going Sinitic cultural morphology. The current linguistic diversity and the dual lingua fracas of English and Mandarin, having caused the current split state of the Sinitic cultural morphology, demonstrate the evolving orientations toward multi-culturalism and universalism.